The present invention relates to vibratory conveyors, and particularly to base-excited vibratory conveyors which include a trough that is spring mounted to a base wherein the base is excited by a vibration driver, and the trough is vibrated through the spring mounting.
Vibratory conveyor devices are in widespread use in view of their versatile material-handling capabilities. Such devices typically include a generally elongated trough or bed that is vibrated by an associated drive system so that material is conveyed along the length of the trough.
A typical two-mass, vibratory conveyor of the base-excited conveyor design includes a trough structure supported on elongate springs extending from a base support structure that is vibrated by an eccentric rotating mass. The vibration is transmitted to the trough through the springs. In typical constructions of two-mass vibratory conveyors, the base support structure of the conveyor includes a pair of longitudinal base members typically constructed from heavy walled tubing or solid plate steel to obtain the desired structural characteristics, and in part to obtain the specific desired weight relationship between the trough and the support structure.
Generally, in operation, the total stroke of the vibrating conveyor is divided between the trough and the base support structure, including the base members, in inverse proportion to their mass ratio. Since it is desirable to minimize the vibratory motion of the support structure to thereby facilitate isolation of the conveyor-transmitted vibration to surrounding structures, the support structure, including the base members, is typically more than twice the weight of the trough structure.
Certain prior art two-mass conveyor designs are configured such that the directed force exciting the conveyor falls on a line aligning the centers of gravity of both the trough and base members of the conveyor, and perpendicular to a face of the drive springs. This design is disclosed in U.S. Pat. No. 4,313,535, for example. This patent discloses a base-excited conveyor having a linear forcing function drive means which generates a force drive line that is co-linear with a line passing substantially through the centers of gravity of the trough mass, conveyor system mass, and the base mass.
As a result of this design approach, it is often necessary, particularly with short conveyors, to add large amounts of weight to the base member such that the plural centers of gravity may be brought into alignment.
In base-excited conveyors, the stroke on the base is dependent on the tuning of the conveyor, and the relationship of the natural frequency of the mass/spring system to the operating frequency of the conveyor. The resultant base weight to trough weight ratio can be in a range of 1.5:1 to 3:1 or more depending on the available force, and how close to resonance it is necessary to tune the conveyor to get the desired trough stroke.
Prior base or support member designs use heavy base beam construction, at considerable cost and weight. Some prior designs not only employ the heavy base design but also uses a separate motor driven dual shaft exciter that is comprised of many components and is costly to produce in limited quantity. In some of the prior art designs that use the dual rotary vibrators, if one of the vibrators should fail, the resulting unbalance could cause structural failure of the conveyor.
In some prior art designs the rotary vibrators are mounted externally on the conveyor base members, on opposite sides of the base and with the eccentrics rotating about parallel, tilted vertical axes. In these conveyors, the entire structure must be stiff enough (four times the operating speed) to have the vibrators synchronize at operating speed. This leads to large costly structures particularly since weight lowers the natural bending frequencies, so stiffness has to be achieved from the member geometry, resulting in the use of large deep members. If the members are not sufficiently stiff, the vibrators tend to lock onto the bending mode frequency so not only will the conveyor not operate properly, but also structural damage could occur as the bending mode is excited.
The present inventor has recognized that it would be advantageous to provide a conveyor design that comprises a minimum of parts. The present inventor has recognized that it would be advantageous to provide a conveyor design whereby the overall weight of the conveyor, and particularly the weight of the base, is minimized. The present inventor has recognized that it would be advantageous to provide a conveyor design that utilizes a compact and economical vibratory exciter and provides an overall economically manufactured design.
The vibratory conveying device embodying the present invention includes a trough for transporting materials and a base underlying the trough. The trough is supported from the base by a plurality of elongated leaf springs. A vibratory exciter or vibratory drive is connected to the base. The base comprises two sheet metal plates or xe2x80x9cwing platesxe2x80x9d arranged in parallel along opposite sides of the conveyor.
According to the invention, the vibratory drive, in the form of dual rotary vibrators, is mounted on a stiff lateral or transverse beam that spans between, and is connected to, the wing plates, such that any natural bending frequency of the stiff lateral beam is at least four times higher than the operating speed of the conveyor. This allows the eccentric weights of the separate vibrators to synchronize, as they operate close to the tuned natural frequency of the conveyor mass spring system, such that the unbalanced forces produced by the rotating eccentric weights of each vibrator add to each other only along the drive line axis and cancel each other out in all other directions.
The use of the stiff mounting beam allows the use of lighter sheet metal construction for the balance of the base members since the wing plates are sufficiently stiff in the direction of the drive line axis, and there are no unbalanced forces produced to excite any bending natural frequencies of the other base members.
The use of the sheet metal construction and the simple construction and assembly of the vibratory exciter using commercially available rotary vibrators, for example using part number C6028 16 vibrators available from Martin Engineering of Neponset, Ill., greatly reduce cost to manufacture the vibratory conveyor. Additionally, in the event that one vibrator should fail in this design, the conveyor would only bounce up and down and feed improperly, since there would be no unbalanced forces effecting bending of the base structural members. Also, the entire exciter package can be dismounted from the conveyor for replacement or repair in one piece, for easy maintenance.
Other features and advantages of the present invention will become readily apparent from the following detailed description and the accompanying drawings.